This set of Organic Chemistry Questions and Answers for Entrance exams focuses on “Macromolecules – 2”.
1. What happens when a macromolecule undergoes hydrolysis reaction?
a) protein coils into its secondary structure
b) the bond between two subunits of a macromolecule is broken
c) a bond is formed between two subunits of a macromolecule
d) water breaks ionic bonds
Explanation: Macromolecules (Polymers) are broken down into monomers in a process known as hydrolysis, which means to split water, a reaction in which a water molecule is used during the breakdown.
2. Which of the following is not a disaccharide?
Explanation: Amylose is a polysaccharide made of α-D-glucose units, bonded to each other through α(1,4) glycosidic bonds.
3. Dehydration and hydrolysis reactions involve removing or adding which of the following to macromolecule subunits?
a) C and O
b) OH and H
c) CH and NH2
d) COOH and H
Explanation: Hydrolysis, which means to split water, a reaction in which a water molecule is used during the breakdown. Dehydration reaction is a chemical reaction that involves the loss of a water molecule from the reacting molecule.
4. What type of macromolecule carries out catalysis in biological systems?
a) proteins called enzymes
b) carbohydrates called starches
c) lipids called steroids
d) nucleic acids called DNA
Explanation: Enzymes are proteins functioning as catalysts that speed up reactions by lowering the activation energy. A simple and succinct definition of an enzyme is that it is a biological catalyst that accelerates a chemical reaction without altering its equilibrium.
5. Amino acids and proteins are ionized at typical biological pH such that both the amino group and the carboxyl group gain hydrogen ions to become -NH3+ and -COOH, respectively.
Explanation: An amino acid has both a basic amine group and an acidic carboxylic acid group. There is an internal transfer of a hydrogen ion from the -COOH group to the -NH2 group to leave an ion with both a negative charge and a positive charge, called as zwitterion. If we increase the pH of a solution of an amino acid by adding hydroxide ions, the hydrogen ion is removed from the -NH3+ group. If we decrease the pH by adding an acid to a solution of an amino acid, the -COO– part of the zwitterion picks up a hydrogen ion.
6. What are the most diverse macromolecules in the cell?
b) mineral salts
Explanation: Proteins show enormous diversity because of different proportions and sequences of 20 amino acids within the protein molecule. Proteins are the most abundant and most varied of the macromolecules having one or more polypeptides (chains of amino acids). The proteins constitute almost 50% of the total dry weight of the cell.
7. In which of the following groups are all polysaccharides?
a) sucrose, glucose and fructose
b) maltose, lactose and fructose
c) glycogen, sucrose and maltose
d) glycogen, cellulose and starch
Explanation: Polysaccharides are complex long chain carbohydrates which are formed by dehydrate synthesis or polymerisation of more than 10 but generally very large number of units called monosaccharide. Starch, glycogen and cellulose are all polysaccharides.
8. Cellulose is the most important constituent of plant cell wall. What are its constituents?
a) branched chain of glucose molecules linked by (3-1, 4 glycosidic bond in straight chain and a-1, 6 glycosidic bond at the site of branching
b) unbranched chain of glucose molecules linked by (3-1, 4 glycosidic bond)
c) branched chain of glucose molecules linked by a-1, 6 glycosidic bond at the site of branching
d) unbranched chain of glucose molecules linked by a-1, 4 glycosidic bond
Explanation: Cellulose molecule is composed of 1600 to 6000 glucose molecules joined together. Those polymers form long twisting macromolecules of cellulose. The chains are unbranched and linear, which are linked by 3-1, 4 glycosidic bond.
9. Lipids are insoluble in water because of which of the following reason?
a) lipid molecules are hydrophilic
b) lipid molecules are hydrophobic
c) lipid molecules are neutral
d) lipid molecules are zwitterions
Explanation: Insolubility of lipids in water is due to the fact that the polar groups they contain are
much smaller than their nonpolar portions. The nonpolar chains are long complex hydrophobic hydrocarbon chains. If shaken in water lipids often form small droplets or micelles.
10. Macromolecules like Enzymes, vitamins and hormones can be classified into a single category of biological chemicals. Why?
a) all of these help in regulating metabolism
b) all of these are exclusively synthesized in the body of a living organism as at present
c) all of these are conjugated proteins
d) all of these enhance oxidative metabolism
Explanation: A conjugated protein is a protein that functions in interaction with other (non-polypeptide) chemical groups attached by bonding or weak interactions. Enzymes, vitamins and hormones are conjugate proteins.
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